1. Field of the Invention
The present invention relates to a printing apparatus having a thermal head that is divided into a plurality of blocks and can make a printing operation by energizing every each block, a memory that stores data for control of the printing apparatus and a control unit that performs printing control, and more particularly to a printing apparatus that can make a printing operation by selecting a suitable printing constant speed based upon a printing line.
2. Description of the Related Art
In a printing apparatus wherein print data composed of printing lines to be printed in one printing operation by a line of heating elements is stored in a print buffer, a thermal head is divided into a plurality of blocks and a printing operation is made by energizing every each block, the number of the block that is to be energized is increased or decreased according to the number of dots of the printing lines in the print data stored in the print buffer, thereby performing a printing on a printing medium.
There is a technique disclosed in Japanese patent application laid-open No. S61-65665 (1986-65665)) as a technique relating to such a printing apparatus. However, in the printing apparatus disclosed in the Japanese patent application '665, a division is made according to the print dot number for one line of heating elements to thereby perform a printing operation, so that a time for energizing the heating elements has to be secured for every number of blocks. Accordingly, the energizing time to the heating elements is required as the divided block number increases, thereby taking much time for obtaining one printed matter. Further, an extremely complicated process is required in order to make a printing operation according to the print dot number, thereby taking also much time for this process. These factors reduce a printing speed, thereby entailing a problem of taking much time for one printed matter.
Moreover, a printing speed is changed according to the number of each block, which causes excessive torque exerted on a paper feed motor for transporting a printing medium. This is a cause of wear and breakdown of the paper feed motor. There is a fear that the service life of the printing apparatus is shortened with the wear or breakdown of the paper feed motor.